363-206-295
Maintenance Description
Issue 1 December 1997 9-17
provisionable holdoff delay and a fixed 15-second clear delay. Yellow signals are
not subject to holdoff or clear delays. Circuit pack failures (except control circuit
pack failures) are subject to the provisionable holdoff and clear delays. Refer to
the set-attr-alm and
rtrv-attr-alm commands in Section 11, "Commands and Reports."
Protection Switching 9
The DDM-2000 OC-12 Multiplexer provides equipment protection switching of all
transmission and synchronization circuit packs and uses SONET standard
automatic protection switching for the OC-3 and OC-12 lines. Installation of
protection switching equipment is optional. Protection switching occurs in
response to automatically detected faults in the circuit packs or OC-3 and OC-12
lines as well as external commands from a technician at a local/remote CIT or
TL1/X.25 message-based OS interface. The DDM-2000 OC-12 Multiplexer uses
SONET protection switching priorities for all transmission protection groups. Refer
to the switch-line, switch-fn, switch-sync, and switch-tsi commands
in Section 11, "Commands and Reports."
Automatic Line Protection 9
The DDM-2000 OC-12 Multiplexer uses the optional SONET 1+1 unidirectional
nonrevertive automatic protection switch (APS) procedures. This means that after
a cut service fiber is repaired, a location does not switch back (revert) and select
the service set as its active fiber/OLIU set.
Status of ACTIVE LED on OLIUs 9
Figure 9-5 illustrates examples of unidirectional and nonrevertive line protection
switches. Note the squares at locations A and C. Each square represents the
transmit or receive section of an OLIU. Figure 9-5(a) and Figure 9-5(b) are
associated with the Service (S) OLIU and Figure 9-5(d) and Figure 9-5(e) with the
Protection (P) OLIU. Four optical fibers are associated with the Service and
Protection OLIUs that interconnect the OLIUs at locations A and C. The two fibers
connecting the Service OLIUs are the service fibers, and the two fibers
connecting the Protection OLIUs are the protection fibers. Fibers and OLIUs
shown in bold are active and carrying service.
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